The present invention relates to a high frequency amplifier which relaxes a drop in base potential of a bipolar transistor upon the input of a bulk power high frequency signal to thereby provide a high saturation characteristic.
The present invention also relates to a high frequency amplifier and a frequency mixer each of which relaxes a drop in base potential of a bipolar transistor upon input of a bulk power high frequency signal to thereby provide a high saturation characteristic and reduce degradation in a noise figure.
A conventional common emitter two stage type high frequency amplifier described in, for example, xe2x80x9cIEEE Microwave Theory and Technology Symposium (1997) Preliminary Reports is one in that a DC bias produced from a current mirror circuit is supplied to a base terminal of a bipolar transistor as shown in FIG. 1.
In the drawing, reference numeral 1 indicates an input terminal for a high frequency signal, reference numeral 2 indicates an output terminal for the high frequency signal, reference numerals 3 indicate amplifying bipolar transistors whose emitter terminals are grounded, reference numeral 4 indicates a constant voltage source, reference numerals 8 indicate bias feed inductors for supplying a DC bias from the constant voltage source 4e to collector terminals of the amplifying bipolar transistors 3, reference numeral 9 indicates a bypass capacitor for short circuiting the high frequency signal, reference numeral 11 indicates a bias bipolar transistor, reference numeral 12 indicates a current mirror bias circuit, reference numerals 15 indicate bias feed resistors for supplying a DC bias from the current mirror bias circuit 12 to base terminals of the amplifying transistors 3, reference numerals 16 indicate DC cut capacitors, reference numerals 19 indicate bias resistors, and reference numerals 28 indicate emitter loaded inductances.
The operation will next be described.
The conventional high frequency amplifier shown in FIG. 1 amplifies the high frequency signal input from the input terminal 1 by the amplifying bipolar transistors 3 and takes out it from the output terminal 2. In order to operate the amplifying bipolar transistors 3, there is a need to supply DC biases to the collector and base terminals of the amplifying bipolar transistors 3. The collector terminals thereof are supplied with the DC bias from the constant voltage source 4e via the bias feed inductors 8, whereas the base terminals thereof are supplied with the DC bias from the current mirror bias circuit 12 via the bias feed resistors 15.
In the above described conventional high frequency amplifier, a bias current supplied from the current mirror circuit increases with an increase in the base current of each amplifying bipolar transistor upon input of the bulk power high frequency signal. Therefore, the high frequency amplifier is accompanied by a problem that a voltage drop is developed across each bias feed resistor so that a base potential of each amplifying bipolar transistor is reduced, thereby degrading a saturation characteristic.
Further, a conventional common emitter high frequency amplifier described in, for example, Preliminary Reports of Communications Society Conference of the Institute of Electronics, Information and Communication Engineers (2001) is one in that a DC bias is supplied from a current mirror bias circuit and one diode switch to a base terminal of a bipolar transistor as shown in FIG. 2.
In the drawing, reference numeral 101 indicates an input terminal for a high frequency signal, reference numeral 102 indicates an output terminal for the high frequency signal, reference numeral 103 indicates an amplifying bipolar transistor emitter terminal of which is grounded, reference numerals 104a and 104b indicate constant current sources, reference numeral 105a indicates a constant voltage source, reference numerals 106a and 106b indicate bias bipolar transistors, reference numeral 107 indicates a bias feed resistor for supplying the DC bias to the base terminal of the amplifying bipolar transistor 103, reference numerals 108a and 108b indicate bias resistors, reference numeral 109 indicates a current mirror bias circuit which comprises the constant current source 104a, the constant voltage source 105a, the bias bipolar transistors 106a and 106b, the bias feed resistor 107 and the bias resistors 108a and 108b, reference numeral 112a indicates a switch bipolar transistor, reference numerals 113a and 113b indicate reference voltage bipolar transistors, and reference numeral 111 indicates a base bias compensating circuit which comprises the constant voltage source 104b, the switch bipolar transistor 112a and the reference voltage bipolar transistors 113a and 113b. 
The operation will now be described below.
The conventional high frequency amplifier shown in FIG. 2 is one in that the high frequency signal input from the input terminal 101 is amplified by the amplifying bipolar transistor 103, followed by extraction thereof from the output terminal 102. When the high frequency signal power input to the input terminal 101 is sufficiently low, i.e., upon a linear operation of the amplifying bipolar transistor 103, the DC bias to the base terminal of the amplifying bipolar transistor 103 is supplied mainly from the current mirror bias circuit 109. When the high frequency signal power input to the input terminal 101 is high, i.e., upon a non linear operation of the amplifying bipolar transistor 103, the DC bias is mainly supplied from the base bias compensating circuit 111. Therefore, an improvement in saturation characteristic is performed by relaxing a drop in base potential VBE of the amplifying bipolar transistor 103 with an increase in the high frequency signal power.
The operation of the base bias compensating circuit 111 will now be described below.
The switch bipolar transistor 112a is a diode switch whose base terminal and collector terminals are short circuit connected. Such a switch is turned on/off by a difference in potential between the emitter terminal and the collector/base terminals. When the switch is turned on, a current flows between the collector and emitter thereof, whereas when it is turned off, no current ideally flows. Here, a voltage to be required for turning on the switch (Hereinafter refereed to as xe2x80x9con voltage of the switchxe2x80x9d) is defined as VSW_ON.
Upon turning off of the diode switch, a current IREF1 generated by the constant current source 104b flows into the two reference voltage generating bipolar transistors 113a and 113b whose base terminals and collector terminals are short circuit connected. Owing to the current IREF1, a voltage of VREF is produced at the base/collector terminal of the reference voltage bipolar transistor 113a. 
When the diode switch is turned off, i.e., a condition VSW_ON greater than VREFxe2x88x92VBE is established with respect to the base potential VBE of the amplifying bipolar transistor 103, no current flows from the base bias compensating circuit 111 to the base terminal of the amplifying bipolar transistor 103.
On the other hand, when the diode switch is turned on, i.e., a condition VSW_ON less than VREFxe2x88x92VBE is established, a current flows between the collector and emitter of the switch bipolar transistor 112a and it is supplied to the base terminal of the amplifying bipolar transistor 103 as a DC bias.
As described above, the base bias compensating circuit 111 supplies the DC bias to the base terminal as it is driven by the base potential VBE of the amplifying bipolar transistor 103, i.e., in response that the power of the high frequency signal input to the input terminal 101 increases.
In the above described conventional high frequency amplifier, though the drop in base potential is relaxed by virtue of an increase in the amount of supply of the current to the base terminal of the amplifying bipolar transistor by the base bias compensating circuit upon input of the bulk power high frequency signal to thereby enhance the saturation characteristic, whereas it is accompanied by a problem that the impedance of the base bias compensating circuit is lowered in accordance with the increase in the amount of supply of the current, thereby degrading a noise figure.
The present invention has been made to solve such a problem as described above (as in the conventional example shown in FIG. 1) and aims to realize a high frequency amplifier and a frequency mixer each of which relaxes a drop in base potential of a bipolar transistor upon input of a bulk power high frequency signal to thereby provide a high saturation characteristic.
Further, the present invention has been made to solve such a problem as described above (as in the conventional example shown in FIG. 2) and aims to implement a high frequency amplifier and a frequency mixer each of which relaxes a drop in base potential of a bipolar transistor upon input of a bulk power high frequency signal to thereby provide a high saturation characteristic and reduce degradation in a noise figure.
A high frequency amplifier according to the present invention is one in which a common emitter bipolar transistor is used, and a constant current source and a constant voltage source are switched to apply a DC bias to a base terminal of the bipolar transistor in accordance with a power level of a high frequency signal input to the bipolar transistor or a power level of a high frequency signal output therefrom.
Because of this arrangement, an effect is brought about by that a high frequency amplifier can be obtained which simultaneously satisfies high resistance to a change in power supply voltage and variations in the characteristic of a transistor which is an advantage at a constant current operation, and a high saturation characteristic which is an advantage at a constant voltage operation.
A high frequency amplifier according to the present invention is one in that the constant current source is always connected to its corresponding base terminal.
Because of this arrangement, an effect is brought about by that a high frequency amplifier can be obtained which simultaneously satisfies high resistance to a change in power supply voltage and variations in the characteristic of a transistor, which is an advantage at a constant current operation, and a high saturation characteristic which is an advantage at a constant voltage operation. Also an effect is brought about by that since the constant current source is always connected to the base terminal, biasing from the constant current source is performed even upon switching between the constant current source and the constant voltage source in accordance with the transition of the amplifying bipolar transistor from its linear operation to its non-linear operation and the transition thereof from the non-linear operation to the linear operation, whereby the base potential of the transistor is biased stably.
A high frequency amplifier according to the present invention is one in that the constant voltage source is connected to the base terminal of the bipolar transistor through a resistor.
Because of this arrangement, an effect is brought about by that a high frequency amplifier can be obtained which simultaneously satisfies high resistance to a change in power supply voltage and variations in the characteristic of a transistor, which is an advantage at a constant current operation, and a high saturation characteristic which is an advantage at a constant voltage operation. Also an effect is brought about by that a threshold value for starting the supply of a bias from the constant voltage source can be changed by changing the voltage of the constant voltage source.
A high frequency amplifier according to the present invention is one in that a DC bias is supplied to a base terminal of the bipolar transistor by a current mirror bias circuit, and a base bias compensating circuit which comprises a constant current source and a switch driven by a base potential and one terminal of the switch is connected to the base terminal of the bipolar transistor and the other terminal thereof is connected to the constant current source, is provided at the base terminal of the bipolar transistor.
Because of this arrangement, an effect is brought about by that a high frequency amplifier can be obtained which relaxes a drop in base potential of an amplifying bipolar transistor in accordance with the input of a bulk power high frequency signal and provides a high saturation characteristic.
A high frequency amplifier according to the present invention is one in that the constant current source constituting the base bias compensating circuit is implemented by a resistor and a constant voltage source, said switch is configured as a diode switch in which a base and collector of a bipolar transistor are short-circuit connected, an emitter terminal of the diode switch is connected to the base terminal of the common emitter bipolar transistor, a collector/base terminals thereof are connected to the resistor, and a reference voltage for the diode switch is supplied from series-connected diode switches more than at least one.
Because of this arrangement, an effect is brought about by that a high frequency amplifier can be obtained which relaxes a drop in base potential of an amplifying bipolar transistor in accordance with the input of a bulk power high frequency signal and provides a high saturation characteristic. Also an effect is brought about by that since IREF, VREF and VSWON of the base bias compensating circuit in the high frequency amplifier can be arbitrarily set according to the resistance value of a bias resistor, the size of a reference voltage bipolar transistor, and the size of a switch bipolar transistor, respectively, a switching threshold value of the base bias compensating circuit can be changed.
A high frequency amplifier according to the present invention is one in that the base bias compensating circuit is connected to the base terminal of the common emitter bipolar transistor through a resistor.
Because of this arrangement, an effect is brought about by that the impedance of the base bias compensating circuit as viewed from the base terminal increases and hence degradation of a noise figure of the high frequency amplifier can be suppressed.
A high frequency amplifier according to the present invention is one in that a DC bias voltage is supplied through a resister to a base terminal of the bipolar transistor by a current mirror bias circuit, and a base bias compensating circuit which comprises a constant current source and a switch driven by a base potential and one terminal of the switch is connected to the constant current source and the base terminal of the bipolar transistor and the other terminal thereof is grounded, is provided at the base terminal of the bipolar transistor.
Because of this arrangement, an effect is brought about by that a high frequency amplifier can be obtained which relaxes a drop in base potential of an amplifying bipolar transistor in accordance with the input of a bulk power high frequency signal and provides a high saturation characteristic.
A high frequency amplifier according to the present invention is one in that a constant current source constituting a base bias compensating circuit is implemented by a resistor and a constant voltage source, a switch is configured as a diode switch in which a base and collector of a bipolar transistor are short-circuit connected, collector/base terminals of the diode switch are connected to the base terminal of the common emitter bipolar transistor, and an emitter terminal thereof is grounded.
Because of this arrangement, an effect is brought about by that a high frequency amplifier can be obtained which relaxes a drop in base potential of an amplifying bipolar transistor in accordance with the input of a bulk power high frequency signal and provides a high saturation characteristic. Also an effect is brought about by that since VSWON of the base bias compensating circuit can be changed by changing the number of switch bipolar transistors, a switching threshold value of the base bias compensating circuit can be changed.
A high frequency amplifier according to the present invention is one in that the base bias compensating circuit is connected to the base terminal of a common emitter bipolar transistor through a resistor.
Because of this arrangement, an effect is brought about by that the impedance of the base bias compensating circuit as viewed from the base terminal increases and hence degradation of a noise figure of the high frequency amplifier can be suppressed.
A frequency mixer according to the present invention is one in that a DC bias is applied to a base of at least one of a bipolar transistor for the input of a high frequency signal and a bipolar transistor for the input of a local oscillation wave by using a configuration for applying the DC bias in the high frequency amplifier according to the present invention.
Because of this arrangement, an effect is brought about by that a frequency mixer can be obtained which simultaneously satisfies high resistance to a change in power supply voltage and variations in the characteristic of a transistor, which is an advantage at a constant current operation, and a high saturation characteristic which is an advantage at a constant voltage operation.
A high frequency amplifier according to the present invention is one in that a common emitter bipolar transistor is used and a DC bias is supplied to abase terminal of the bipolar transistor by a current mirror bias circuit, characterized in that a base bias compensating circuit which comprises a constant current source and series-connected two switches driven by a base potential of the bipolar transistor and one terminal of the series-connected switches is connected to the base terminal of the bipolar transistor and the other terminal thereof is connected to the constant current source, is provided.
Because of this arrangement, an effect is brought about by that a high frequency amplifier can be obtained which relaxes a drop in base potential of an amplifying bipolar transistor in accordance with the input of a bulk power high frequency signal and provides a high saturation characteristic. That is to say, an effect is brought about by that when a high frequency signal having low power is input, a constant current operation which shows low dependency on a change in power supply voltage and being good against a process variations of each transistor is achieved by the DC bias supplied mainly from the current mirror bias circuit, and when a bulk power high frequency signal is input, a constant voltage operation which shows a high saturation characteristic is achieved by the DC bias supplied mainly from the base bias compensating circuit, then both can be implemented simultaneously.
Further, an effect is brought about by that since the impedance can be increased by connecting selector switches in series, degradation in a noise figure can be reduced.
A high frequency amplifier according to the present invention is one in that a constant current source constituting the base bias compensating circuit is implemented by a resistor and a constant voltage source, each of said switches is configured as a diode switch in which a base and collector of a bipolar transistor are short-circuit connected, an emitter terminal of the first diode switch thereof and collector/base terminals of the second diode switch thereof are connected in series, an emitter terminal of the second diode switch is connected to the base terminal of the common emitter bipolar transistor, collector/base terminals of the first diode switch are connected to the resistor, and a reference voltage for the diode switches is supplied from series-connected diode switches more than at least one.
Because of this arrangement, an effect is brought about by that a high frequency amplifier can be obtained which relaxes a drop in base potential of an amplifying bipolar transistor in accordance with the input of a bulk power high frequency signal and provides a high saturation characteristic. That is to say, an effect is brought about by that when a high frequency signal having low power is input, a constant current operation which shows low dependency on a change in power supply voltage and being good against a process variations of each transistor is achieved by the DC bias supplied mainly from the current mirror bias circuit, and when a bulk power high frequency signal is input, a constant voltage operation which shows a high saturation characteristic is achieved by the DC bias supplied mainly from the base bias compensating circuit, then both can be implemented simultaneously.
Further, an effect is brought about by that since the impedance can be increased by connecting selector switches in series, degradation in a noise figure can be reduced.
A high frequency amplifier according to the present invention is one in that a common emitter bipolar transistor is used and a DC bias is supplied to abase terminal of the bipolar transistor by a constant current source and a resistor characterized in that a base bias compensating circuit which comprises a constant current source and at least one switch driven by a base potential of the bipolar transistor and one terminal of the switch is connected to the base terminal of the bipolar transistor and the other terminal thereof is connected to the constant current source, is provided.
Because of this arrangement, an effect is brought about by that when a high frequency signal having low power is input, a constant current operation which shows low dependency on a change in power supply voltage and being good against a process variations of each transistor is achieved by the DC bias supplied mainly from the current mirror bias circuit, and when a bulk power high frequency signal is input, a constant voltage operation which shows a high saturation characteristic is achieved by the DC bias supplied mainly from the base bias compensating circuit, then both can be implemented simultaneously.
A high frequency amplifier according to the present invention is one which a common emitter bipolar transistor is used and a DC bias is supplied to a base terminal of the bipolar transistor by a current mirror bias circuit, characterized in that an emitter terminal of a base bias compensating bipolar transistor whose collector terminal and base terminal are connected to a constant voltage source, is connected to the base terminal of the common emitter bipolar transistor.
Because of this arrangement, an effect is brought about by that when a high frequency signal having low power is input, a constant current operation which shows low dependency on a change in power supply voltage and being good against a process variations of each transistor is achieved by the DC bias supplied mainly from the current mirror bias circuit, and when a bulk power high frequency signal is input, a constant voltage operation which shows a high saturation characteristic is achieved by the DC bias supplied mainly from the base bias compensating circuit, then both can be implemented simultaneously.
Further, an effect is brought about by that since an idle current at the input of a small-power high frequency signal, which flows in each reference voltage bipolar transistor becomes unnecessary, current consumption can be reduced.
A high frequency amplifier according to the present invention is one in that a constant voltage source connected to the base terminal of the base bias compensating bipolar transistor comprises a constant current source and at least one diode switch or more, each having collector/base terminals short-circuit connected.
Because of this arrangement, an effect is brought about by that a base bias compensating circuit can be made resistant to variations in power supply.
A high frequency amplifier according to the present invention is one in that a diode switch whose collector/base terminals are short-circuited, is inserted between the emitter terminal of the base bias compensating bipolar transistor and the base terminal of the common emitter bipolar transistor.
Because of this arrangement, an effect is brought about by that a decrease in the impedance of a base bias compensating circuit as viewed from an amplifying bipolar transistor can be relaxed which occurs when the current flows from the base bias compensating circuit to the base terminal of the amplifying bipolar transistor upon input of a bulk power high frequency signal, whereby degradation in a noise factor can be reduced.
A high frequency amplifier according to the present invention is one in that a resistor is inserted between an emitter terminal of the base bias compensating bipolar transistor and a base terminal of the common emitter bipolar transistor.
Because of this arrangement, an effect is brought about by that a decrease in the impedance of a base bias compensating circuit as viewed from an amplifying bipolar transistor can be relaxed which occurs when the current flows from the base bias compensating circuit to the base terminal of the amplifying bipolar transistor upon input of a bulk power high frequency signal, whereby degradation in a noise factor can be reduced.
A frequency mixer according to the present invention is one in that the above described base DC bias applying configuration of the above described high frequency amplifier is applied to at least one of a bipolar transistor for the input of a high frequency signal and a bipolar transistor for the input of a local oscillation wave.
Because of this arrangement, an effect is brought about by that a frequency mixer can be obtained which simultaneously satisfies resistance to a change in power supply voltage and variations in transistor which is an advantage at a constant current operation, and a high saturation characteristic and the effect of reducing degradation in a noise figure, each of which is an advantage at a constant voltage operation.